Ultra-thin slab or thick-strip casting

ABSTRACT

A system of twin-roll casting an ultra-thin slab or thick-strip of metal with a liquid core still present inside the hollow shell of the casting as it exits the nip of the opposing counter rotating casting rolls. The wide sides of the cast shell are formed against a recessed casting surface on each roll and the narrow end walls of the shell are formed against the tapered ends of the recessed area so one half of the narrow end wall is formed on each roll and the two halves are joined together at the nip to form the full perimeter of the metal casting. A liquid-cooled copper mold liner provides continued support to each of the four sides of the casting below the twin-rolls and contact with those chilled copper mold liners continues to remove heat from the liquid core of the casting enabling the shell to continue growing in thickness. As the casting exits the mold it will be of adequate thickness to pass through opposing pairs of support rolls below the mold without bulging where water sprays can provide the additional cooling needed for final and complete solidification. A variation of this system uses one or more separating dams to cast different metals or different alloys of the same metal to integrally cast a dual-layer or multi-layer ultra-thin slab or thick strip of metal with a thin metal layer on one or both of the wide and narrow end casting surfaces.

This is a divisional of Ser. No. 13/186,851, filed Jul. 20, 2011, whichis a nonprovisional of U.S. Provisional Patent Application 61/408,736,filed Nov. 1, 2010. The entirety of both of the aforesaid documents ishereby incorporated by reference as if set forth fully herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This application relates to the field of high speed, high productionmetals casting and more specifically to twin-roll casting of anultra-thin slab or thick strip of solidifying metal with a liquid coreremaining beyond the nip of the twin casting rolls. This applicationfurther relates to a variation of this technology to integrally cast adual-layer or multi-layer ultra-thin slab or thick strip with one ormore surface claddings of a different metal or different alloy of thesame metal on one or both sides of the casting.

2. Description of the Related Technology

In the field of continuous casting of metals several relatively newmethods have been developed to cast a shape that is near that of thefinal net product being produced. “Near-net-shape” casting of a coiledflat product has evolved from casting a thick slab that requires asignificant amount of reduction by hot rolling to casting a thin slabthat requires less rolling, thus saving significant amounts of energy.For coiled materials being rolled to thicknesses less than a fewmillimeters, even thin-slabs require more rolling energy than necessaryto reach the net thickness. Thus thin-strip casting by the twin-rollcasting process is being pursued for very thin metal production.

Another process called “thin-strip” casting is being pursued andpromoted as offering “Energy savings of up to 2.4 million Britishthermal units (Btu) per tonne of steel produced” according to the U.S.Department of Energy fact sheet entitled “Strip Casting: AnticipatingNew Routes to Steel Sheet”. However this casting method produces onlyvery thin sheets of steel up to 3 mm thick. In addition, the throughputfrom a thin-strip caster is less than one third that of a thin-slabcaster. Because the product is so thin to begin with, there is no chanceof achieving the necessary reduction ratios needed for many high-qualitysteel grades.

The drawback of near-net-shape casting of thin strip is low productionthroughput. Whereas a thick slab caster can produce as many as 3 milliontons of steel coils annually on a single strand and a thin-slab castercan produce as many as 1.8 million tons annually on a single strand, athin-strip caster generally produces less than 0.6 million tons annuallyon a single strand. The thin-strip casting limitation that preventshigher production rates is the need for the cast metal to be fullysolidified by the time it leaves the nip or closest point betweenopposing rollers used in the twin-roll casting process. If notsolidified by then the liquid metal rushes out of the pool above the nipand causes the strand shell to bulge below, which can lead to a ruptureor breakout as it is called in the continuous casting industry.Accordingly, the steel industry currently has a huge void when it comesto continuously casting steel in the thickness range between 3 mm (⅛inch) thick and 2-inch thick. As a result the original intent to reduceenergy by rolling thinner slabs has been all-but-forgotten because ofthe desire for greater throughputs.

In order to improve the productivity of the twin-roll casting process, ameans of strand shell support below the rollers is needed to preventbulging normally caused by the ferrostatic pressures within a newlyformed shell with a liquid metal core remaining after the roll nip. Withsuch strand support, the twin-roll spacing could be made wider toproduce a thicker casting that would exit the roller section with asolidified outer shell and a liquid core of molten metal inside thatwould continue solidifying as it travels through the support sectionsbelow. Such a post-roll shell support system is described in PCTInternational Publication Number WO 96/01710 dated 25 Jan. 1996. Itcites, “Immediately downstream of the twin rolls, the cast strand iscooled by directing it through a stationary cooled mold”. Thepublication further describes a preferred casting thickness of 5 to 35mm and a steel throughput rate of 1 to 6 tonnes per minute. That wouldmake the process a hybrid between a thin slab normally 40-90 mm thickand a thin-strip normally 1-5 mm thick caster yet still having a maximumproductivity rate somewhere between thin-slab casting 1.8 million tonsannually and thick-slab casting 3 million tons annually.

What the casting process described in WO 96/01710 fails to describe is asystem for solidifying and supporting the narrow ends of the castproduct to prevent leakage of the molten metal out through the narrowends during casting. Without such means the liquid metal would spill outof the casting as soon as it exits what are described as the “side dams83” causing interruption of the cast and damaging the equipment below.Since side dams, or end dams as other twin-roll operations call them,are generally made of a refractory material that does not function wellas a heat exchanger to promote solidification, one can imagine that thenarrow ends of the cast product would still be molten or if they didsolidify at all they would be V-shaped and would crumple as they arepulled through the nip between the opposing rolls.

SUMMARY OF THE INVENTION

It is an object of this invention to provide a system and method thatwill form one wide side and half of each end wall of the cast shell oneach twin roller so those halves will join together as the casting exitsthe twin-roll section at the nip in order to complete the outerperimeter of the metal casting.

It is further an object of the invention to provide water cooled supportfor both the wide sides and the narrow end walls in the mold below theroller nip to prevent metal leakage from the seam between the narrow endhalves and to promote continued solidification of the product until itexits the mold section or until such time it has adequate thickness tosupport itself without bulging between support rolls below the mold.

It is also an object of one aspect of this invention to simultaneouscast two or three different metals or metal alloys by positioningseparating dams over one or both of the rolls so the initialsolidification on one or both roller surfaces is of one or another metalor metal alloy and after it passes by the tip of the separating damsubsequent solidification occurs from a different liquid metal pool ofanother metal or metal alloy thus forming a multilayer metallicstructure.

In order to achieve the above and other objects of the invention, a twinroll continuous casting system according to a first aspect of theinvention includes first and second casting rolls; and a recessed rollersurface on at least one of the first and second casting rolls forforming at least a portion of a casting shell.

A method of continuously casting a metal material according to a secondaspect of the invention includes steps of providing a molten metalmaterial; and cooling the molten metal material into a solid castingusing a casting roller that has a recess defined therein.

A twin roll continuous casting system according to a third aspect of theinvention includes first and second casting rolls that are constructedand arranged to form a casting shell; and support structure positionedbeneath the casting rolls for supporting substantially an entireperimeter of the casting shell as viewed in transverse cross-section.

A twin roll continuous casting system according to a fourth aspect ofthe invention includes a cavity that is constructed and arranged to holda liquid metal pool; first and second casting rolls; at least twoseparating dams positioned axially within the cavity for separating thecavity into at least three separate metal pools; wherein differentmaterials may be cast simultaneously in at least three layers into asingle casting shell.

A twin roll continuous casting system according to a fifth aspect of theinvention includes a cavity that is constructed and arranged to hold aliquid metal pool; at least one separating dam positioned within thecavity for separating the cavity into at least two separate metal poolsof different materials; and first and second casting rolls for receivingmaterial from the at least two separate metal pools and casting at leasta first layer having a first thickness and a second layer having asecond thickness into a single casting shell, and wherein a ratio of thefirst and second thicknesses is substantially within a range of about1:2 to about 1:40.

These and various other advantages and features of novelty thatcharacterize the invention are pointed out with particularity in theclaims annexed hereto and forming a part hereof. However, for a betterunderstanding of the invention, its advantages, and the objects obtainedby its use, reference should be made to the drawings which form afurther part hereof, and to the accompanying descriptive matter, inwhich there is illustrated and described a preferred embodiment of theinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatical depiction of a system for casting anultra-thin slab or thick-strip using the twin-roll casting process withthe wide side casting surface of each roller recessed into the outerroll diameter to a depth equal to one half of the cast thickness. Thephantom line on each roll represents the depth of that wide side castingsurface on each roll, which is further illustrated by the correspondingthickness of the cast slab exiting from the bottom being equal to thedistance between the recessed surfaces of the two rolls.

FIG. 2 is a diagrammatical depiction of that system as viewed from thecenter looking toward one end. In this view the wide side castingsurface can be seen with a solidifying surface that begins at theuppermost location of the molten metal pool continuing to grow inthickness toward the nip and beyond as the casting loses heat first tothe cooled roll and afterwards to the cooled mold below. This view alsodepicts the liquid core in the center of the casting that has not yetsolidified at the bottom extremity of this view.

FIG. 3 is a diagrammatical depiction of that system as viewed with theliquid metal removed to illustrate solidification of the metal againstthe end walls of the recessed area and the joining of the two halves ofthe casting at the roll nip.

FIG. 4 is a diagrammatical depiction of the ultra-thin slab orthick-strip shape as it exits the twin-roll section of the caster. Thisview illustrates the radius on each corner of the cast slab and theangle formed by the junction between the wide side casting surface andthe end wall casting surface. This view further illustrates the jointwhere each half of the end walls meets to complete the outer perimeterof the metal casting.

FIG. 5 is a diagrammatical depiction of the casting system viewed fromabove to illustrate the liquid metal pool in the center and how itcontacts the end wall sections of each roller to begin solidification ofthe end walls simultaneously with the beginning of solidification of thewide sides of the casting. Also illustrated in this view is the positionof the side dams on top of the raised ends of the dog-bone shaped rollsto contain the ends of the liquid metal pool.

FIG. 6 is a diagrammatical depiction of the casting system viewed fromthe end to illustrate both the wide side support below the rolls and thenarrow end support that begins slightly below the nip between the outerdiameters of the casting rolls.

FIG. 7 is a diagrammatical depiction of the casting system viewed fromthe wide side to illustrate the wide side support by the mold directlybelow the rolls, the continued support by rollers below the mold, andthe mold end wall support members in position to both support and coolthe narrow ends of the ultra-thin slab or thick-strip casting.

FIG. 8 is a diagrammatical depiction of the casting system viewed fromthe end to illustrate a means of separating two liquid metal pools inorder to integrally cast two different metals or metal alloys to form adual-layer ultra-thin slab or thick-strip casting.

FIG. 9 is a diagrammatical depiction of the casting system viewed fromthe end to illustrate a means of separating three liquid metal pools inorder to integrally cast two or three different metals or metal alloysto form a multi-layer ultra-thin slab or thick-strip casting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designatecorresponding structure throughout the views, and referring inparticular to FIG. 1, the ultra-thin slab or thick-strip 1 is partiallysolidified against a recessed casting surface 2 on each of two opposing,counter rotating rolls 3 and 4 and exits through the opening defined atthe nip 5 by the recessed surfaces on the wide side and the inner edgesof the recess on each roll, which form the narrow ends of the casting.

The maximum depth of the recess on each roll may be different. However,the two rolls preferably have recesses of the same maximum depth. In apreferred embodiment, the maximum depth of the recess on a casting rollis substantially one half of the casting thickness.

A side dam 6 is used at each end of the twin-roll assembly to contain aliquid pool of molten metal, which is continuously fed into the spacebetween the upper portions of the two opposing rolls. Downward pressureexerted on side dam 6 forces it against the outer diameter 7 of eachroll forming a seal to prevent metal leakage. The side dam 6 ispreferably preheated before casting to prevent any of the incoming metalfrom solidifying against its inner surface thus limiting shell formationto the recessed casting surface 2 and the inner edges of the recessedareas.

As the cast shell reaches the nip 5, the two opposing edges of shellthat solidified against the inner edges of the recess are broughttogether to form the end wall at each end of the casting, thus formingthe perimeter of the casting. The point where they contact forms acontinuous seam 8 between the two halves of the casting and continuedsolidification of the liquid core inside the hollow shell seals the seam8 from the inside, preventing any leakage.

FIG. 2 illustrates a view through the center of the casting lookingtoward one end. The liquid metal pool 9 loses heat to the liquid-cooledrolls 3 and 4, causing the metal to crystallize or solidify against thecooled exposed surfaces it comes into contact with. As additional heatis transferred by conduction to the liquid-cooled rolls 3 and 4, thesolidifying shell 10 of the wide side becomes thick enough at the nip 5to span the short distance to the mold 11, below where additional heatis extracted and the shell becomes thicker still. The mold 11 is alsoliquid-cooled and consists of two wide side copper liners 12 and twonarrow end copper liners 13 in FIG. 7 that support and cool theperimeter of the shell. The wide side copper liner is mounted to waterjacket 14 that internally directs the cooling liquid in and out of thecopper liner 12 and provides structural support. The top of the mold ismanufactured with a radius that matches up to the lower portion of therecessed casting surface 2 and is distanced from that surface byclearance gap 15. The top of the copper mold liners 12 & 13 have a smallentry taper 16 to assure a smooth transition of the ultra-thin slab orthick-strip from the twin-roll section to the mold 11.

The initial point of solidification 17 for the wide side of the castingoccurs near the top of the liquid metal pool 9, where it first contactsthe recessed casting surface 2 on each roll. The solidifying shell 10continues to grow thicker as it travels down through the machine untilsuch time as it has completely solidified. Unlike thin-strip produced ontwin-roll casters, which is completely solidified by time it passesthrough the nip 5 between the rolls, the ultra-thin slab or thick-striphas a liquid core 18 as it passes through the nip 5 and may have aliquid core 18 as it leaves the bottom of the mold 11. This is madepossible by the support and continued cooling that occurs below thetwin-roll section.

FIG. 3 is a view through the casting with the liquid metal removed andthe rolls stopped. It illustrates how the ends of the ultra-thin slab orthick-strip 1 are formed against the inner edges of the recessed areas,which are referred to in this drawing as the narrow end casting surfaces19 of the rolls 3 and 4. The initial point of solidification for eachnarrow end wall half 20 begins at the top of the liquid metal pool 9shown on this drawing as height 21. No solidification occurs against theside dam 6 that presses against the outer diameter 7 of each roll. Thusthe two narrow end wall halves 22 solidify against the narrow endcasting surfaces 19 and are joined together at the nip 5 to connect thetwo halves of the casting at the seam 8 completing the perimeter of theultra-thick slab or thick-strip 1.

Further illustrated in FIG. 3 is the solidifying shell 10 of the wideside against the recessed casting surface 2 and how it gains thicknessas it travels down through the machine. Also shown is the solidifyingshell 23 of the narrow end, and how the seam disappears from viewslightly below the nip 5 as new metal solidifies against the insidesurface and it too becomes thicker as it moves down through the machine.

FIG. 4 is a bottom view of the ultra-thin slab or thick-strip 1 exitingthe nip between the dog bone-shaped twin-rolls 3 and 4. A radius 24 atthe transition from the recessed casting surface 2 to the narrow endcasting surface 19 results in the rounded corners 25 formed on thecasting. The radius 24 is a size proportional to the design castingthickness, preferably not exceeding 50% of the casting thickness. Themore preferred range for the radius 24 is between 0.1 and 0.33 of thecasting thickness. But most preferably, the radius 24 is in a range from0.2 to 0.3 of casting thickness. The angle 26 of that transition betweenthe recessed casting surface 2 and the narrow end casting surface 19that terminates at the outer diameter of the roll 7 must be greater than90 degrees but less than 130 degrees to allow separation of the castingfrom rollers 3 and 4 immediately following exit of the casting throughthe roll nip 5 without impeding any drag forces upon the narrow ends ofthe cast product. Preferably the angle will range between 100 and 120degrees.

For example if the design casting thickness is to be 20 mm thick, theradius in this corner would be no more than 25% of 20 mm or 5.0 mm. Thatleaves 10 mm of area between the radii for the seam connecting the twohalves of the ultra-thin slab or thick strip casting. The corner radiusmay be as small as 10% of the design casting thickness leaving up to 80%of the area between the radii for the seam connecting the two halves ofthe ultra-thin slab or thick strip casting.

Further illustrated in FIG. 4 is the presence of the liquid core 18between the solidifying shells 10 of the wide sides as the castingleaves the roll nip 5. Ordinarily this is not possible with twin-rollcasting, because ferrostatic pressure exerted from the liquid pool ofmetal above would cause the shell to bulge outward from the center. Butthis system uses copper mold liners on both the wide sides 12 on FIG. 2and the narrow ends 13 on FIG. 7 to provide continued shell supportbelow the nip 5 of the twin rolls. As a result the wide side 27 of thecasting and the narrow end 28 of the casting continue to grow inthickness as heat from the liquid core 18 is transferred into theliquid-cooled copper mold liners. In addition the seam 8 between the twohalves of the narrow end 28 of the casting quickly becomes sealed fromthe inside as new metal from the liquid core 18 solidifies against theinner shell surfaces below the nip 5.

FIG. 5 is a top view above twin-rolls 3 and 4 showing the liquid metalpool 9 between the two rolls and the two side dams 6. The initial pointof solidification 17 for the wide sides 27 of the casting begins at thetop of the liquid metal pool 9 where it meets the recessed castingsurface 2. The initial point of solidification for the narrow end wallhalf 20 begins where the liquid metal pool 9 meets the narrow endcasting surface 19. The depth of the recessed casting surface 2, theradius 24 in the corner, and the angle 26 between the recessed castingsurface 2 and the narrow end casting surface 19 that terminates at theouter diameter 7 of the roll dictates the shape of the narrow end wallhalves 22 on FIG. 3 and the corners 25 on FIG. 4 of the casting. Theangle 26 may be in a range that is substantially about 90° to about130°, preferably from 100° to 120°.

FIG. 6 is an end view of the ultra-thin slab or thick-strip 1 exitingthe bottom of the mold 11 illustrating the pointed shape of the narrowend mold water jacket 29 and the identical shape of the narrow end moldcopper liner 13 in FIG. 7, which is shielded from view in this drawing.Also shown is the close proximity of the upper portion of the narrow endmold water jacket 29 to the outer diameter 7 of the rolls 3 and 4 andhow they are separated only by a small narrow end clearance gap 30 belowthe nip 5. The width of the narrow end water jacket 29 and narrow endcopper 13 in FIG. 7 is shown to be approximately the same as thedistance between the recessed casting surfaces 2 of the two rolls.However they may become wider toward the back on very thin castings foradded structural support. Also shown in this view are the wide sidecopper liners 12 of the mold and the wide side water jackets 14 of themold on either side of the casting. Above the outer diameter 7 of thetwin rolls 3 and 4 can be seen the side dam 6 that contains the liquidmetal pool above the rolls.

FIG. 7 is a side view of the ultra-thin slab or thin-strip 1 castingcoming through the mold 11 and entering a post-mold roll support section31 below made up of support rolls 32 with bearing blocks 33 at each toallow the support rolls 32 to rotate while supporting the wide side ofthe casting 27 traveling out from the bottom of the mold 11. Between themold and the first support roll 32 as well as between additional supportrolls 32 is a gap 34 for spray water to access the surface of thecasting to provide additional cooling and to promote the finalsolidification of the casting.

This view also shows the narrow end mold copper liner 13 attached to thenarrow end water jacket 29 supporting the narrow end of the casting 28as it passes through the mold 11 from just below the nip 5 to the bottomof the mold 11. This view also shows the back of the wide side moldwater jacket 14 that has the wide side mold copper liner 12 on FIG. 2mounted to the front supporting the wide side of the casting 27. Thecopper mold liners may have a casting surface that has a hard surfacecoating to minimize wear. The hard surface coating preferably has ahardness that is substantially within a range of about 250 to about 1200Vickers, more preferably substantially within a range of about 500 toabout 1200 Vickers and most preferably substantially within a range ofabout 800 to about 1200 Vickers.

With two wide side and two narrow ends supported, the entire perimeterof the casting is substantially supported by copper mold liners. A gap34 at the corners between copper liners may be present as there islittle need to support the rounded corner of the casting 25 whichnaturally benefits from two-dimensional cooling of the corners. Such agap 34 could be right at the corner or slightly off the corner in eitherdirection in the mold.

FIG. 8 is an end view of a dual-layer ultra-thin slab or thick-strip 35being cast, with a separating dam 36 isolating the primary pool ofmolten metal 9 from a secondary liquid metal pool 37 of a differentmolten metal or different alloy of the same molten metal that forms acladding 38 on one surface. This variation of the twin-roll castingprocess that is described in U.S. patent application Ser. No. 12/539,333filed on 11 Aug. 2009 and its continuation Ser. No. 12/626,818, filed on27 Nov. 2009, both of which are incorporated by reference as if setforth fully herein, results in a thinner layer of a second metal beingformed on one side of the dual-layer ultra-thick slab of thick-strip 35.The location of the separating dam 36 can be varied along the contactarea between roll 4 and the liquid metal pool 9, and the secondaryliquid metal pool 37 to control the cladding 38 thickness. The closerthe separating dam 36 is to the initial solidification point 17 thethinner the cladding 38 is on the final dual-layer ultra-thick slab orthick-strip casting 35. Additional solidification of the dual-layercasting after it passes the separating dam 36 occurs from the primaryliquid metal pool 9 beginning at the secondary initial point ofsolidification 39 on that side of the casting.

The thickness of each side of the dual-layer metal is preferablysubstantially within a range of about 1:2 to about 1:40, more preferablysubstantially within a range of about 1:3 to about 1:35 and mostpreferably substantially within a range of about 1:4 to about 1:30. Inother words, 1 mm of one metal alloy clad onto 40 mm of a second metalalloy could be used to cast a clad dual-layer ultra-thin slab or thickstrip.

The ratio of cladding 38 thickness to the remainder of the dual-layerultra-thin slab or thick-strip 35 thickness formed from the primaryliquid metal pool 9 can be varied from 1:2 to 1:40 by varying thelocation of the separating dam 36 position and varying the gap betweenthe two rolls 3 and 4.

The casting process could also be altered by positioning a separatingdam over each of the two rolls to form three liquid metal pools forcasting a multi-layer metal. This would produce thickness ratios betweenthree layers from about 1:1:1 to as high as 1:40:1 whereby the center ofthe multi-layer metal alloy would generally constitute the majority ofthe thickness of the multi-layer ultra-thin slab or thick strip. Oneexample of using the process would be to cast a thin cladding orstainless steel layer on each side of a carbon steel core thus gettingthe benefit of the corrosion-resistant stainless steel on each surfacewith the cost and strength benefits of having the less expensive andstronger carbon steel in the center of the multi-layer ultra-thin slabor thick strip. Preferably, an austenitic stainless steel in the 300series would be used for maximum corrosion resistance. The outer layercould alternatively be a material such as zinc or copper. As anotheralternative, the core layer could be a lightweight metal such asaluminum, while the cladding layer is a material such as carbon steel orstainless steel.

FIG. 9 is an end view of a multi-layer ultra-thin slab or thick-strip 40being cast with separating dams 36 isolating the primary pool of moltenmetal 9 from a secondary liquid metal pool 37 and a third liquid metalpool 41 of different molten metals or different alloys of the samemolten metal that form cladding 38 on one side of the casting from thesecondary liquid metal pool 37 and cladding 42 on the opposite side ofthe casting from the third liquid metal pool 41. Details of thisembodiment are the same as those described in FIG. 8 but applied to bothsides of the multi-layer ultra-thin slab or thick-strip 40 casting toform cladding 38 on one side and cladding 42 on the other side of amulti-layer ultra-thin slab or thick-strip 40.

The ratio of cladding thicknesses to the remainder of the multi-layerultra-thin slab or thick-strip 40 thickness formed from the primaryliquid metal pool 9 can be varied by changing the location of theseparating dam 36 positions as described in FIG. 8 and the gaps betweenthe two rolls 3 and 4. This would produce thickness ratios from 1:1:1 toas high as 1:40:1 whereby the center of the multi-layer metal alloyformed from the primary liquid metal pool 9 would generally constitutethe majority of the thickness of the multi-layer ultra-thin slab orthick strip 40. In other words, the ratio of the thickness of the centercore layer to the thickness of either or both of the outer layers couldbe substantially within a range of about 1:1 to about 40:1. Morepreferably, such a ratio would be substantially within a range of about1:3 to about 1:35 and most preferably substantially within a range ofabout 1:4 to about 1:30.

By providing a means to solidify not only the side walls of the castingin the twin-roll process but the narrow end walls as well, the fullperimeter of the ultra-thin slab or thick-strip will be formed thusforming a full shell around a liquid core of molten metal. This willenable casting speeds to range from 6 meters per minute to as high as100 meters per minute depending on the final thickness of the product.Preferably the casting speeds will range from 8 meters per minutecasting 35 mm thick ultra-thin slabs to 80 meters per minute casting 5mm thick strip.

The system in the present invention may be used to make a variety ofsteel or alloy products. For example, the system shown in FIG. 9 iscapable of making three layer ultra-thin slab or thick strip 40 that issuitable for applications where steel corrosion is a significantconcern, such as pipelines. Corrosion of steel always occurs throughoxidation at its surface where the carbon steel comes into directcontact with oxygen. One common solution to steel corrosion is usingstainless steel where large amounts of very expensive metals such asnickel and chrome are pre-alloyed into the steel. The problem withstainless steel is its high cost, which makes it cost-prohibitive andimpractical for most applications. In addition, stainless steel tends tohave less strength than other steels so it may not be suitable forapplications that normally require high-strength steels.

The system in FIG. 9 may be used to make steel that has a stainlesssteel cladding 42 yet with normal steel core. Such “hybrid” steel willhave a layer of stainless steel on the surface to resist corrosion and acore of low-cost or high-strength steel. Such hybrid steel is an idealmaterial to provide high strength support in an environment in whichsteel corrosion is a significant concern, such as pipelines.

An ultra-thin slab or thick strip produced according to the inventioncould also be used to produce a multilayer material such as armor formilitary vehicles. In this embodiment, the first layer may be made up ofa material such as a hard, high carbon steel with superior strength,while the second layer may be a softer, low carbon steel.

It is to be understood, however, that even though numerouscharacteristics and advantages of the present invention have been setforth in the foregoing description, together with details of thestructure and function of the invention, the disclosure is illustrativeonly, and changes may be made in detail, especially in matters of shape,size and arrangement of parts within the principles of the invention tothe full extent indicated by the broad general meaning of the terms inwhich the appended claims are expressed.

What is claimed is:
 1. A twin roll continuous casting system,comprising: first and second casting rolls that are constructed andarranged to form a casting shell; and support structure positionedbeneath the casting rolls for supporting substantially an entireperimeter of the casting shell as viewed in transverse cross-section. 2.A twin roll continuous casting system according to claim 1, wherein saidsupport structure comprises copper.
 3. A twin roll continuous castingsystem according to claim 1, wherein said support structure is liquidcooled.
 4. A twin roll continuous casting system according to claim 1,wherein the support structure is constructed and arranged to facilitatecontinued solidification of the casting shell.
 5. A twin roll continuouscasting system according to claim 1, wherein the support structureincludes a hard surface coating to minimize wear, the hard surfacecoating having a hardness that is substantially within a range of about250 to about 1200 Vickers.
 6. A twin roll continuous casting systemaccording to claim 1, wherein the support structure includes a firstsupport surface for supporting a narrow end of the casting shell, andwherein the first support surface is tapered at an upper portionthereof.
 7. A twin roll continuous casting system according to claim 6,wherein portions of the first support surface beneath the upper portionare substantially flat.
 8. A twin roll continuous casting systemaccording to claim 1, wherein the tapered upper portion of the firstsupport surface terminates at a point.
 9. A twin roll continuous castingsystem according to claim 6, wherein the first support surface forms anarrow gap with respect to one of the first and second casting rolls.10. A twin roll continuous casting system according to claim 1, whereinthe first and second casting rolls are constructed and arranged to forma casting that has a liquid core beneath the casting rolls.
 11. Acontinuous casting system for making an ultra-thin or thick stripcasting, comprising: casting roll means for forming a casting shellhaving pair of narrowfaces and a pair of widefaces, the casting shellhaving a thickness that is within a range of 0.125 inch to 2 inches andhaving a liquid core beneath a nip of the casting roll means; andsupport structure positioned beneath the casting rolls for supportingsubstantially an entire perimeter of the casting shell as viewed intransverse cross-section.
 12. A continuous casting system for making anultra-thin or thick strip casting according to claim 11, wherein saidsupport structure comprises copper.
 13. A continuous casting system formaking an ultra-thin or thick strip casting according to claim 11,wherein said support structure is liquid cooled.
 14. A continuouscasting system for making an ultra-thin or thick strip casting accordingto claim 11, wherein the support structure is constructed and arrangedto facilitate continued solidification of the casting shell.
 15. Acontinuous casting system for making an ultra-thin or thick stripcasting according to claim 11, wherein the support structure includes ahard surface coating to minimize wear, the hard surface coating having ahardness that is substantially within a range of about 250 to about 1200Vickers.
 16. A continuous casting system for making an ultra-thin orthick strip casting according to claim 11, wherein the support structureincludes a first support surface for supporting a narrow end of thecasting shell, and wherein the first support surface is tapered at anupper portion thereof.
 17. A continuous casting system for making anultra-thin or thick strip casting according to claim 16, whereinportions of the first support surface beneath the upper portion aresubstantially flat.
 18. A continuous casting system for making anultra-thin or thick strip casting according to claim 11, wherein thetapered upper portion of the first support surface terminates at apoint.
 19. A continuous casting system for making an ultra-thin or thickstrip casting according to claim 16, wherein the first support surfaceforms a narrow gap with respect to one of the first and second castingrolls.